Generally, hinges for doors are classified into hinges operating manually and free hinges for automatically closing the doors open through a spring, hydraulic pressure, or a combination of the two.
According to the conventional hinges, the door becomes closed by means of elasticity of the spring after has been open, and at this time, the elasticity of the spring is constantly maintained through the hydraulic pressure, so that the door can be slowly closed.
According to the conventional spring hinges, further, if the door is open, the spring built in the hinge is compressed, and if it is desired that the door is closed, the compressed spring at the time when the door has been open is restored to its original position, so that the door becomes closed.
According to the conventional hinges, however, the degree of elasticity of the spring is generally adjusted in the unit of a click interval of a clutch, thereby making it impossible to precisely adjust the degree of elasticity of the spring.
Particularly, a diameter of a rotary shaft of the conventional hinge is limitedly designed so that it is almost impossible to set tight click intervals.
Moreover, the spring used for the hinge is a twist spring, and accordingly, the degree of elasticity of the twist spring is not adjusted in such a manner as to be wound or unwound by the number of turns thereof, but adjusted to a given angle range due to the changes in diameters and the limitation in the diameter of the rotary shaft, so that it is almost impossible to precisely adjust the degree of elasticity of the twist spring to the unit of click.
So as to solve the above-mentioned problems, accordingly, a hinge for opening/closing a door has been proposed in Korean Patent Application Laid-open No. 10-2013-0131036 (Dated Dec. 3, 2013) filed by the same applicant as the invention. According to the conventional hinge for opening/closing a door, the degree of elasticity of the twist spring is finely adjusted, but due to the opening/closing of the door, the finely adjusted state of the twist spring is released so that the degree of elasticity of the twist spring has to be frequently adjusted again.